Molecular imprinting is a technique devised to generate a polymeric material that is analyte specific. The analyte can be any organic molecule, biological or macromolecule. Molecular imprinting has been used to prepare materials that recognize proteins or other biological compounds, especially where the structural information needed for rational design is lacking. Likewise, if a natural receptor is poorly characterized or difficult to isolate, artificially prepared mimics may serve as a useful alternative. Furthermore, such polymers are considerably less costly to produce when compared to, e.g., antibodies and receptors.
Antibodies are used in several areas, such as therapy, immunoaffinity and purification. Of particular interest is the use of antibodies in immunoassays. However, antibodies for these procedures are normally produced by immunizing animals with the corresponding antigen leading to polyclonal antibodies, or by using fused cells (B cells) allowing the obtained cell lines to produce monoclonal antibodies.
As an alternative, some non-biologically derived antibody mimics or artificial antibodies have been described. For example, the anti-theophylline and anti-diazepam polymers, i.e., mimics, prepared in accordance with the teachings of PCT Application WO 94/11403, the entirety of which is incorporated herein by reference. Such polymer structures are similar to biological antibodies in binding and recognizing antigens and avoid the need for animal sources. These antibody mimics are especially useful where it is difficult or impossible to raise antibodies.
The object of creating artificial counterparts to natural macromolecular binding entities, such as proteins, is of great interest. Employing natural macromolecules in rough environments such as high temperatures and pressures (e.g., sterilization conditions) is of major concern for many applications because of their natural sensitive properties. Furthermore, the efficiency and selectivity exerted by, e.g., receptors interacting with agonists and antagonists or antibodies recognizing antigens, is difficult to reproduce in synthetic systems [1]. Molecular imprinting provides an alternative to other approaches such as sophisticated procedures used in the field of supramolecular chemistry [2].
The rapidly mushrooming field of molecular imprinting is derived from the concept of creating designed recognition sites in macromolecular matrices by means of template polymerization [3-7]. Molecularly imprinted polymers have been shown to possess remarkable recognition properties that have been used in various fields such as drug separations [8-10], receptor mimics [11-14], bio-mimetic sensors [15], antibody mimics [16], template-assisted synthesis [17] and catalysis [18-19].
Of particular interest are the corticosteroids produced in the adrenal cortex and possess numerous and wide-spread effects in vivo. For example, the corticosteroids influence (1) metabolism, (2) electrolyte and water balance, (3) anti-inflammatory action, and (4) functions of the nervous system [20]. Many medical analyses where corticosteroids are of concern, e.g., in the assessment of the functional status of the adrenal cortex, utilize antibody-based assay methods such as RIA and ELISA for the selective recognition of a desired corticosteroid [21]. However, in addition to the general biological interest of steroid interactions with, e.g., antibodies and receptors, these substances are potentially useful for the study of molecular recognition phenomena [22]. The rigid structure of the fused ring system leads to a minimized number of conformations that the molecules may adopt in the interactions with recognition matrices resulting in higher binding strength since the entropy loss in binding is smaller [23] and a multitude of structurally very closely resembling structures are available. However, the limited number of polar interacting points necessary for non-covalent interactions inevitably leads to a decreased binding performance, and molecularly imprinted polymers against steroids have previously only been acquired using strong covalent binding systems such as carboxylic esters and carbonic acid esters [17,24].
Thus, a need exists for molecularly imprinted polymers (MIPs) that selectively recognizing steroid structures, steroid hormones, and in particular, steroids such as cortisol and corticosterone based steroids.